The present invention relates to electric machines.
Electric machines are used for several different purposes in modern vehicles. For example, electric machines are commonly employed as starters, alternators, traction motors and for other purposes. In these applications, the electric machine may act as a motor, generator or be selectively operable as either a motor or a generator.
There is an increasing demand for electric machines used in vehicle applications, as well as other non-vehicular applications, for an electric machine with reduced size and increased efficiency. Improvements in electric machine design which allow for cost efficient manufacture while meeting the increasingly stringent demands of modern vehicular applications are desirable.
FIG. 1 is a schematic view of end turns 120 extending in an axial direction from laminations 122 of a stator of the prior art. Laminations 122 have a radially outer surface 124 and a radially inner surface 126 and defines a central opening encircled by the radially inner surface 126. End turns 120 are part of winding wires wherein that all have the same length for a wrap of the winding regardless of which layer in which the wrap is disposed. A wrap, as used herein, refers to that portion of a winding wire that extends for 360 degrees about the stator core. After insertion of the windings into the slots of laminations 122, the heights of end turns 120 progressively vary from a radially outermost end turn 120a, which has the smallest height to a radially innermost end turn 120h, which has the largest height. End turn 120a may be said to be in a first layer and end turn 120h may be said to be in an eighth layer. The difference in heights of end turns 120 is due to the circumferential distance between slots being greater the more radially outward the winding layer is disposed. Thus, the radially outermost winding layer spans the longest circumferential distance between slots and has the shortest length available for end turn height. Because the radially outermost winding must have at least a minimum end turn height in order to clear the lamination, the more radially inward windings which span a shorter circumferential length have greater end turn heights. As a result, the heights of the radially inward layers can be excessively large or greater than ideal.
FIG. 2 is a schematic view of end turns 220 extending in an axial direction from laminations 222 of another stator of the prior art. Laminations 222 have a radially outer surface 224 and a radially inner surface 226 and defines a central opening encircled by the radially inner surface 226. End turns 220 are part of windings or wires that all have different lengths so that, after insertion of the windings into the slots of laminations 222, the heights of end turns 220 are all equal. A wrap in the radially outermost layer has the largest length, and a wrap in the radially innermost winding has the shortest length. Although this design is efficient from a winding material perspective, having wires of different lengths makes manufacturing more complicated and costly.